diff --git a/chrome/android/java/src/org/chromium/chrome/browser/customtabs/content/WebAppLaunchHandler.java b/chrome/android/java/src/org/chromium/chrome/browser/customtabs/content/WebAppLaunchHandler.java
index c896c8e6550f4..eea03e39b0e26 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/customtabs/content/WebAppLaunchHandler.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/customtabs/content/WebAppLaunchHandler.java
@@ -16,6 +16,7 @@ import static org.chromium.build.NullUtil.assumeNonNull;
 import android.app.Activity;
 import android.content.ActivityNotFoundException;
 import android.content.Intent;
+import android.content.pm.ProviderInfo;
 import android.net.Uri;
 import android.text.TextUtils;
 
@@ -260,7 +261,30 @@ public class WebAppLaunchHandler extends WebContentsObserver {
         /* This method can be called for file handling intent as well. In this case we need to send
         a file data extras as well. Also we need to grant file permissions */
         if (fileData != null && !fileData.uris.isEmpty()) {
+            // SECURITY: |fileData.uris| comes directly from EXTRA_FILE_HANDLING_DATA on the
+            // incoming intent and is fully attacker-controlled. |packageName| is the
+            // Binder-verified caller package -- correct, but that means we're granting TO the
+            // attacker. A malicious app can supply content://<chrome-pkg>.FileProvider/... URIs
+            // here and receive a READ+WRITE grant to Chrome's private cache (passwords/,
+            // net-export/, pdfs/, webapks/, Offline Pages/archives/) because ChromeFileProvider
+            // declares android:grantUriPermissions="true".
+            //
+            // Bandaid: refuse to grant any URI whose authority resolves to a provider in
+            // Chrome's own package. The legitimate file-handling use case never involves
+            // Chrome-owned URIs -- the TWA app shares URIs from its OWN provider for Chrome
+            // to forward back. (A proper fix should also gate this whole branch on Digital
+            // Asset Links verification having succeeded, and probably drop the WRITE flag.)
+            String selfPkg = mActivity.getPackageName();
             for (Uri uri : fileData.uris) {
+                String auth = uri.getAuthority();
+                if (auth != null) {
+                    ProviderInfo pi =
+                            mActivity.getPackageManager().resolveContentProvider(auth, 0);
+                    if (pi != null && selfPkg.equals(pi.packageName)) {
+                        Log.w(TAG, "Refusing to grant Chrome-owned URI to caller: " + uri);
+                        continue;
+                    }
+                }
                 mActivity.grantUriPermission(
                         packageName,
                         uri,